An engine appropriately mixes air and fuel and generates driving power by burning the mixed gas. In order to obtain required output power and combustion efficiency, sufficient air should be supplied to the engine. For this, a turbocharger may be used to increase combustion efficiency and supply sufficient, or additional, air to the engine.
Generally, a turbine of a turbocharger is rotated by pressure of exhaust gas exhausted from the engine, a compressor of the turbocharger compresses fresh air flowing in from the outside, and the compressed air is supplied to a combustion chamber of the engine. The turbocharger has been applied to most diesel engines, and has recently been applied to gasoline engines.
The turbocharger includes a waste gate valve that adjusts an exhaust gas amount supplied to the turbine from the cylinder. However, the waste gate valve used for the turbocharger may be expensive.
As another example, an electric supercharger compresses external air using a compressor operated by a motor. Since the electric supercharger is operated by the motor, there is little turbo lag. The electric supercharger mainly supplies compressed air to the cylinder in a low speed and low load region.
The turbocharger (hereinafter referred to as a ‘mechanical turbocharger’, if necessary) operated by exhaust gas has low responsiveness, and there is much remaining gas in a combustion chamber because of high back pressure. Thus, abnormal combustions, such as knocking or pre-ignition in the combustion chamber, may occur in the combustion chamber, so it is difficult to realize the engine having a high compression ratio.
Further, the electric supercharger has high responsiveness, but output of a motor of the electric supercharger is limited by a limitation of an electric system of a vehicle. So boosting by the electric supercharger is mainly limited to a low-speed and a middle-speed region.
Therefore, in an engine having the mechanical turbocharger and the electric supercharger, an apparatus for controlling the engine that can improve fuel consumption by realizing a high compression ratio is required.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.